The present invention disclosed herein relates to a patch antenna with wide bandwidth at millimeter wave band, and more particularly, to a high-gain, high-efficiency, wideband millimeter wave band patch antenna constructed on a multi-layer substrate.
Frequencies of the millimeter wave band are more straightforward and have wideband characteristics as compared with those of micro wave band, thereby drawing attention in application to radars and communication services. Particularly, since wavelengths of the millimeter wave band are short, it is easy to manufacture small antennas and thus reduce system sizes largely. Among communication services in the millimeter wave band, 60-GHz broadband communication services and 77-GHz vehicle radar services have been fairly commercialized, and products thereof are now available on the market.
To provide small and inexpensive products by using the merits of millimeter wave band systems, much research is being conducted on system on package (SOP) systems. Among methods of constructing such SOPs, a method of using a low temperature co-fired ceramic (LTCC) or liquid crystal polymer (LCP) technique is considered to be one of most suitable methods. According to an LTCC or LCP technique, basically, a multi-layer substrate is used, and passive devices such as a capacitor, an inductor, and a filter are built in the substrate, so that small and inexpensive modules can be provided. Another merit of using such a multi-layer substrate is that cavities can be freely formed, and thus the freedom of module configuration increases.
In the structure of an SOP system, an antenna patch is considered to a core element determining the system performance. In the case of a patch antenna operating in the millimeter wave band, particularly, ultrahigh frequency band of 60 GHz or higher, signal leakage occurs in the form of surface waves propagating along the surface of a dielectric substrate of the patch antenna. Such signal leakage increases as the thickness of the substrate increases and the dielectric constant of the substrate increases. Such signal leakage decreases the radiation efficiency and gain of the patch antenna. Although 60-GHz band communication systems require a wide bandwidth of 7 GHz or wider, it is difficult to satisfy such requirement by using a typical patch antenna structure.
Current commercial millimeter wave band modules have an SOP structure constructed by using an LTCC technique to reduce manufacturing costs. However, a ceramic substrate such as an LTCC substrate has higher dielectric constant than an organic substrate, and thus, if the ceramic substrate is used to form the patch antenna, since the radiation efficiency and gain of the patch antenna are low as described above, the number of antenna arrays should be much increased to obtain desired antenna gain, and it is difficult to obtain desired wideband characteristics. Therefore, commercial products are manufactured in a manner such that only antenna patches are formed of organic substrates having low dielectric constant. Thus, the size and manufacturing costs of modules are increased as compared with the case where the entire system including the antenna patch is mounted on an LTCC substrate in the form of an SOP.